1. Field of the Invention
This invention relates generally to digital integrated circuit fabrication, and in particular, to an apparatus and method wherein conductive patterns are written in amorphous silicon or polysilicon and used for interconnecting circuit elements of the integrated circuit.
2. Description of the Related Technology
Integrated circuits have revolutionized the field of electronics by making possible a level of technological sophistication unknown in the days of vacuum tubes and even discrete transistors. An integrated circuit may comprise, on a small silicon chip, many thousand or even a million or more transistors, including associated diodes, resistors and capacitors, interconnected together to form complex electronic functions. These interconnections may be made by metal deposited in patterns during one or more manufacturing process steps during the fabrication of the integrated circuit chip.
The metal patterns normally are fabricated using masks that determine the shape and size of the metal pattern. When these masks are defective, the resulting metal pattern may also be defective. Sometimes, however, it is possible to interrupt the normal manufacturing process to add or delete conductive paths when the metal pattern is found to be missing or deposited improperly. A defective integrated circuit chip may be reworked by removing protective layers to expose the defective metal areas. Removal of unwanted metal may be done by etching or other means well known in the art. New metal patterns may then be deposited to replace missing metal interconnections.
Thin metal lines may be deposited utilizing an integrated circuit fabrication technology called Focused Ion Beam or FIB deposition. The FIB deposition system may be used to deposit thin metal lines to form a metal pattern in the exposed rework area of the integrated circuit chip needing repair. The FIB deposition system, however, may take tens of hours to deposit a single small metal line because the deposition time is determined by the FIB column fluence. The FIB fluence is the number of atoms of metal that can flow down the ion beam column during a given time. Therefore, repair of defective integrated circuit chip metal connection patterns is extremely time consuming and expensive. What is needed is a way of repairing or replacing defective conductive metal patterns on an integrated circuit chip in a rapid and cost effective manner.